Does a center of pressure(CP) utility exist in OpenFOAM? I have not been able to find anything. Secondly, does anyone know how to manipulate the fields in order to determine CP as a post processing activity.

I tried using the moments and forces generated using the forces utility to find CP, however, the calculated positions are not located anywhere on my body.

Without CP, the calculated forces are useless when it comes to structural stress calcs.

Ok this is how the centre of pressure coordinates (x,y,z) are related to a 3D body.

Mx=-Fy*z+Fz*y
My=Fx*z-Fz*x
Mz=-Fx*y+Fy*x

Simple enough - 3 equations and 3 unknowns. Can someone tell me why using the moments and forces calculated using the Forces utility produces x,y,z values that aren't located anywhere close to the body (wall patch)? Where is the error being introduced? Both the moments and forces are calculated using the shear stress and pressure on the body.

Can someone pppplease chime in? Thanks!

Last edited by Greg Givogue; April 27, 2011 at 20:07.
Reason: corrected signs in equations

Thanks for the suggestion but that is for coefficient of pressure and not center of pressure. Center of pressure(CP) is bit more involved because it involves the position of each cell (x) on the surface.

I can calculate CP but I can't get coordinates x y z for CP that actually lie on the surface of the body. I'm also not sure why there's a difference between the forces utility and patchIntegrate results...

The reason why the pressure force found using patchIntegrate and the forces utility are different is because the fluid density was set to 1.225 in the forces utility while the patchIntegrate used a density of 1.

Not sure if this will help, but you can extract the pressure values for each cell on the surface in their normal components by following the steps below in Paraview.

Extract Surfaces
Generate Surface Normals
Use the calculator to multiply pressure by the surface normals (Normals*p)

This then prints the values in the data tab at the right in three columns, one for each normal direction.

I then integrate these to get total forces on the area using Integrate Variables, BUT...

In the calculator though there will be options to calculate the normals multiplied by pressure individually in the three components, which you can then use in your equation to specify the centre of pressure.

If you get this working please let us know the next couple of steps. I'm short of time otherwise I'd try it myself.

Thanks very much,I have read that post before.
and now I use a force and moment to equivalent the resultant force and the moment get from surface integral

but how to choose a radius in FEM with the structural analysis, and use the force to form the moment is the problem, especially when in time this resultant force and moment change ,then the point change

I want to use a fixed point and change the components of the force to equivalent to this